My mother died . before her death she obtained a law firm to make a will. ( Irrev Trust dtd ) on May 28, 2019.How do I find out the name of law firm?

Please accept my condolences on the loss of your mother. A Will is not an irrevocable trust, so it's not clear to me what the reference to "Irrev Trust dtd" is your question is for. A Will and a trust are two different documents, although a Will can provide for the creation of a trust. Depending on how the document your mother had prepared was drafted, you may not have a lot of rights to receive information about it, especially if the document is a trust, rather than a Will. A person who creates a trust has the right to prevent beneficiaries from becoming entitled to receive much information about the trust. If you really are a beneficiary, you'll eventually receive something, but you may never be given all of the information you might want to see. If your mother DID have a Will, however, and if that Will has been offered for probate (which may or may not have been necessary, depending on what your mother owned and how she owned it), then you can contact the probate court for the county where she had her principal residence (I am assuming she also lived in Georgia- if not, then this answer may not be correct) and ask them to send you a copy of the Will and anything else that has been submitted for her probate. You'll need to pay for the copy, but it's not that expensive.  As for finding the law firm that prepared her Will, if you aren't the nominated Executor, then the law firm likely won't be able to provide you with information directly unless the Executor says that they can, so I wouldn't waste a lot of time trying to figure out who they were right now. Unfortunately, if your sister is not providing you with information, you may need to hire your own attorney, one with estate litigation experience, and have the attorney send her a letter demanding information. This is especially true if no Will has even been offered for probate, because you can't get information from the probate court if they don't have it. Get a consultation. Best wishes to you.